Saving van Gogh for future generations

Some of the bright yellows in the paintings of renowned Dutch painter Vincent van Gogh and those of his contemporaries are in danger of fading and darkening to brown, and scientists are working to discover the cause of the degradation and to find ways to preserve the brilliant hues for future generations.

Van Gogh (1853-1890) abandoned realistic detail and pursued art that evoked a more direct visual and emotional response, partly caused by the vivid colors he chose. Thanks to major innovations in pigment manufacturing in the 19th century, he was able to employ bright yellow chrome paint in his great oeuvre of self-portraits, landscapes and sunflower paintings.

An international team recently used a microscopic x-ray beam to reveal a complex chemical reaction taking place in the very thin layer where the paint meets the varnish. Ironically, they found that sunlight, a major source of inspiration for van Gogh, triggers a chemical reaction that turns chrome yellow into brown. Their results suggest that shielding this particular type of chrome yellow paint from UV light and sunlight will help to preserve it. But not all period paintings are affected; nor does the degradation always happen at the same speed.

X-rays were used to study why the paintings of Vincent van Gogh are losing their brilliance. At the top is a photo of his painting Bank of the Seine (1887), divided in three and artificially colored to simulate a possible state of preservation in 1887 (at left) and 2050 (at right). At the lower left is a microscopic sample from art masterpieces molded in plexiglass blocks. The tube with yellow chrome paint is left over from the historical period. On the lower right is an x-ray microscope set up at the European Synchrotron Radiation Facility with a sample block ready for a scan. In the center is an image made using a high-resolution analytical electron microscope to show affected pigment grains from the van Gogh painting. It shows how the color at the surface has changed due to reduction of chromium. The scale bar indicates the size of these pigments. Courtesy of ESRF/Antwerp University/van Gogh Museum.
The team collected samples from three paint tubes left over from the period and aged them for 500 hours using a UV lamp. Only one sample showed significant darkening. X-ray analysis identified the darkening of the top layer as linked to a reduction of the chromium in the chrome yellow from Cr(VI) to Cr(III). The scientists reproduced the antique paint and found that the darkening effect could be provoked by UV light. The techniques used in the analysis included x-ray diffraction along with spectroscopy methods that use IR radiation, electrons and x-rays.

The same methods were used to examine affected areas on two van Gogh paintings, and the same reduction reaction appears to have occurred.

The team was led by Koen Janssens of Antwerp University in Belgium and Letizia Monico of Perugia University in Italy. The work was conducted partly at ESRF (European Synchrotron Radiation Facility) in Grenoble, France, and at DESY (Deutsches Elektronen Synchrotron) in Hamburg, Germany.

The bending of x-rays by the regular layers of molecules in a crystal acting like a very small diffraction grating. The diffraction pattern so obtained and recorded on film provides a means for analyzing the crystal structure.